The Arabidopsis HKT1 gene homolog mediates inward Na+ currents in Xenopus laevis oocytes and Na+ uptake in Saccharomyces cerevisiae

被引:365
作者
Uozumi, N [1 ]
Kim, EJ
Rubio, F
Yamaguchi, T
Muto, S
Tsuboi, A
Bakker, EP
Nakamura, T
Schroeder, JI
机构
[1] Nagoya Univ, Biosci Ctr, Nagoya, Aichi 4648601, Japan
[2] Univ Calif San Diego, Dept Biol, La Jolla, CA 92093 USA
[3] Univ Calif San Diego, Ctr Genet Mol, La Jolla, CA 92093 USA
[4] Nagoya Univ, Grad Sch Bioagr Sci, Nagoya, Aichi 4648601, Japan
[5] Univ Tokyo, Grad Sch Sci, Dept Biophys & Biochem, Bunkyo Ku, Tokyo 113, Japan
[6] Univ Osnabruck, Abt Mikrobiol, D-49076 Osnabruck, Germany
[7] Chiba Univ, Fac Pharmaceut Sci, Chiba 2638522, Japan
关键词
D O I
10.1104/pp.122.4.1249
中图分类号
Q94 [植物学];
学科分类号
071001 ;
摘要
The Na+-K+ co-transporter HKT1, first isolated from wheat, mediates high-affinity K+ uptake. The function of HKT1 in plants, however, remains to be elucidated, and the isolation of HKT1 homologs from Arabidopsis would further studies of the roles of HKT1 genes in plants. We report here the isolation of a cDNA homologous to HKT1 from Arabidopsis (AtHKT1) and the characterization of its mode of ion transport in heterologous systems. The deduced amino acid sequence of AtHKT1 is 41% identical to that of HKT1, and the hydropathy profiles are very similar. AtHKT1 is expressed in roots and, to a lesser extent, in other tissues. Interestingly, we found that the ion transport properties of AtHKT1 are significantly different from the wheat counterpart. As detected by electrophysiological measurements, AtHKT1 functioned as a selective Na+ uptake transporter in Xenopus laevis oocytes, and the presence of external K+ did not affect the AtHKT1-mediated ion conductance (unlike that of HKT1). When expressed in Saccharomyces cerevisiae, AtHKT1 inhibited growth of the yeast in a medium containing high levels of Na+, which correlates to the large inward Na+ currents found in the oocytes. Furthermore, in contrast to HKT1, AtHKT1 did not complement the growth of yeast cells deficient in K+ uptake when cultured in K+-limiting medium. However, expression of AtHKT1 did rescue Escherichia coli mutants carrying deletions in K+ transporters. The rescue was associated with a less than 2-fold stimulation of K+ uptake into K+-depleted cells. These data demonstrate that AtHKT1 differs in its transport properties from the wheat HKT1, and that AtHKT1 can mediate Na+ and, to a small degree, K+ transport in heterologous expression systems.
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页码:1249 / 1259
页数:11
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